Green’s Dictionary of Slang

(Aus./N.Z.) a euph. for fucking adj.

1919		Aussie (France) XII Mar. 2/1: Tell the bloke who issues the prizes to pull his finger out. If he don’t come to light with a divvy soon, I’ll knock his floppin’ ’ead orf.
1921		(con. WWI) E. Lynch Somme Mud 4: Slit ya floppin’ yellin’ gizzards out, ya flamin’ [...] hyenas.
1943		J.A.W. Bennett ‘Eng. as it is Spoken in N.Z.’ in AS XVIII:2 Apr. 91: There are a large number of words and phrases in common use which one could scarcely classify as confined to, or originating in, New Zealand, but which deserve to be recorded in any attempt to convey something of the flavor of the colloquial speech of the country. Amongst these are [...] flopping, as in ‘a flopping nuisance’.